A heavy burden of drug and alcohol use has been observed among men who have sex with men (MSM) living in South African townships, peri-urban or rural residential areas that were reserved for non-Whites under Apartheid and which are still residential communities for millions of black South Africans today. Our understanding of the determinants of drug and alcohol abuse among MSM living in these townships is limited. Qualitative data suggests that drugs and alcohol are mostly used in social situations and that drinking together is one of a limited number of ways in which MSM interact. Therefore, it is important to explore the influence of social network characteristics on drug and alcohol abuse, in addition to individual risk factors. One potentially harmful effect of drug and alcohol use is sexual risk behavior, which is of heightened importance among MSM in townships as they have high rates of HIV transmission. Thus far, studies that have looked at the relationship between substance use and sexual risk behavior among MSM in townships have reported inconsistent findings. Further research on these topics is needed. This project aims to achieve a more comprehensive understanding of the relationship between substance use and sexual risk behavior among MSM in South African townships by exploring the individual and contextual causes of these co-occurring risk behaviors, and by juxtaposing two distinct temporal perspectives to investigate them. This project will achieve this using data drawn from the NIH-funded study, HIV and Sexual Risk in African MSM in South African Townships. This study used respondent-driven sampling to recruit 480 black MSM from four South African townships in the metropolitan area of Tshwane. A survey using previously validated measures to assess drug use, alcohol use, and sexual risk behavior was administered among these men. A detailed training plan will be followed in order to acquire the methodological skills, substantive knowledge and cross-disciplinary expertise to address the following aims: 1) assess whether social network characteristics predict substance abuse beyond individual risk factors; 2) assess whether substance use predicts sexual risk behavior over the past year, then test whether the relationship between substance use and sexual risk behavior is modified by reasons for substance use, expectations about the effect of substance use on sexual behavior, or intentions to engage in safe sex; 3) assess whether drug or alcohol use during a defined sexual encounter predict sexual risk behavior, after accounting for individual-, situational-, and partnership-level characteristics. A greater understanding of substance use among MSM in South African townships, as well as the link between substance use and sexual risk behavior, will inform the development of interventions to reduce substance abuse and sexual risk behavior among this critical population. Given that South Africa has a high prevalence of hazardous drinking, a growing problem with drug use, and the highest burden of HIV in the world, identifying and addressing factors that contribute to substance abuse and the spread of HIV in South Africa is of critical importance.